by Alan Gomez, USA TODAY

by Alan Gomez, USA TODAY

Want a sign that the economy is on the rebound? Illegal immigration from Mexico is starting to rise again, according to a new report.

Immigration from Mexico fell to historic lows during the worst years of the recession. After four decades that brought 12 million people from Mexico to the U.S., people started heading back home and continued doing so from 2007 to 2011.

It's impossible to pinpoint the exact number of people crossing the southwest border with Mexico, but the study by U.S. and Mexican researchers estimates that immigrants headed north in the first half of 2012 outnumbered those heading back for the first time since 2007.

"Illegal immigration is a market indicator," said Roy Beck, CEO of NumbersUSA, an Arlington, Va.-based think tank that advocates lower levels of legal and illegal immigration. "They all got gigantic networks of family and friends who are already here sending information back and forth. So this is basically another sign that the economy is picking up."

The report is a collaboration between the University of Southern California and El Colegio de la Frontera Norte in Tijuana, a Mexican government-sponsored research group. Researchers used interviews with people along the border and data from the U.S. and Mexico.

Jeffrey Passel, the senior demographer at the non-partisan Pew Hispanic Center who was not involved in the report, said the findings look legitimate. But he said the small increase in people coming from Mexico does not mean the United States is close to the massive influx of illegal immigrants seen recently. For example, in 2000, 770,000 Mexicans immigrated, legally and illegally, to the U.S. In 2010, that number fell to 140,000.

"Right now, we're in a period where Mexican migration to the U.S. is at very low levels," Passel said.

Roberto Suro, a public policy professor at USC and co-author of the report, said people cited the weakening economy and increased enforcement measures for returning to, or staying in, Mexico.

Beck said the renewed rise in illegal immigration is due partly to President Obama's immigration record. He said a new program that could allow up to 1.8 million illegal immigrants brought to the U.S. as children to have their deportations deferred sends a signal that the border remains open.

"The word has gone out that this administration is going to do all it can to keep you from having to leave the country," he said.

Ali Noorani, executive director of the National Immigration Forum, which supported Obama's deportation deferral program, pointed to the fact that Obama has set records for the number of people deported as proof that he's serious about enforcement.

Noorani said the renewed rise in illegal immigration simply shows that the country's legal immigration system remains broken.

"Now that our economy is recovering, the bigger question is: How is our immigration system going to serve a growing economy?" he said.